Abstract: A control rod coupling assembly for coupling a nuclear reactor control rod to a control rod drive mechanism is disclosed. The control rod drive mechanism includes an index tube and a bayonet head. The control rod includes blades and a tube at the intersection of the blades. The control rod coupling assembly includes a bayonet socket configured to receive the bayonet head, a shaft extending from the bayonet socket through the control rod, and a handle extending from the shaft, the handle movable to rotate the bayonet socket without rotation of the control rod.

Abstract: A spring set within a control rod guide tube in a nuclear reactor biases a control rod for movement into the reactor core. The spring set includes at least three springs in series, two being under compression and one in tension. The control rod may be displaced downwardly in a direction away from the core by a cable connected at one end to the control rod support element and at its opposite end to a drum. By winding the cable on the drum, energy is stored in the spring set. During a SCRAM, the drum is released, enabling the spring set to rapidly displace the control rod fully into the core.

Abstract: A hydraulically based control rod drive system that is contained within the pressure vessel is disclosed for positioning the control rods relative to fuel rods positioned in a nuclear core of a boiling water reactor. Hydraulic jacks mounted on an open grid located entirely within the pressure vessel at a position above the nuclear core are used to position the control rods. Suitable jack and grid structures, as well as a hydraulic control arrangements are described.

Abstract: A forced-circulation boiling-water reactor includes fluidic diodes in the coolant fluid return path between the pump deck and the core inlet plenum. The fluidic diodes permit a downstream flow to proceed relatively freely, but substantially resist upstream flow. When pumps are shut down, the fluidic diodes serve to augment natural circulation, thus enhancing core stability. When the pumps are operating, the fluidic diodes serve to resist backflow, minimizing any loss of pump efficiency. This direction-flow asymmetry imposed by the fluidic diodes is achieved without moving parts, so as to achieve a high level of reliability.

Abstract: A latch assembly removably joins a steam separator assembly to a support flange disposed at a top end of a tubular shroud in a nuclear reactor pressure vessel. The assembly includes an annular head having a central portion for supporting the steam separator assembly thereon, and an annular head flange extending around a perimeter thereof for supporting the head to the support flange. A plurality of latches are circumferentially spaced apart around the head flange with each latch having a top end, a latch hook at a bottom end thereof, and a pivot support disposed at an intermediate portion therebetween and pivotally joined to the head flange. The latches are pivoted about the pivot supports for selectively engaging and disengaging the latch hooks with the support flange for fixedly joining the head to the shroud or for allowing removal thereof.

Abstract: A captive fastener is joinable to a stud for being retained in a nuclear reactor. The fastener includes a head fixedly joinable to the stud, and at least one spring clip extending perpendicularly from the head and having a proximal end fixedly joined thereto, and a distal end in the form of hook for retaining the fastener in the reactor. The hook is resiliently deflectable laterally relative to the head for allowing assembly and disassembly.

Abstract: A reactor core removable fuel assembly includes upper and lower tie plates having pluralities of fuel rods and hollow control rods extending therebetween. The lower tie plate includes a lower manifold therein joined in flow communication with a reservoir containing a neutron absorbing control liquid, with the reservoir being removable from the reactor core together with the fuel assembly. The control liquid is selectively pumped from the reservoir through the lower manifold and into the control rods for selectively varying the level of the control liquid therein for controlling reactivity.

Abstract: A nuclear reactor core assembly includes a support plate having a plurality of inlets for channeling water to a core lattice fixedly joined thereto. The lattice includes a plurality of flow channels, each including a respective separately removable fuel bundle. In a preferred embodiment, the core lattice includes a plurality of flow dividers joined together for allowing unrestrained expansion and contraction thereof, and which prevent crossflow of water therebetween.

Abstract: A control rod is selectively positioned in a nuclear reactor core inside a reactor pressure vessel by a drive assembly. The assembly includes a flexible cable releasably joined to the control rod by a coupling. A drive is joined to the cable for selectively advancing and retracting in opposite directions the cable for selectively positioning the control rod in the reactor core. In exemplary embodiments, the drive and cable may be disposed above or below the reactor core. In another embodiment, a pressurized driving fluid may be used to additionally position the control rod within the reactor core.

Abstract: A forced-circulation boiling-water reactor includes bypass check valves between a downcomer and a core inlet plenum. When the recirculation pumps are operating at full capacity, there is a maximum pressure differential from the downcomer to the core inlet plenum. This pressure differential keeps the valves closed so that recirculating fluid is constrained to flow through the pumps. When the pumps are not operating, a driving water head in the downcomer forces the valves open, augmenting the flow cross section between the downcomer and the core inlet plenum, enhancing natural circulation. The enhanced natural circulation provides greater core stability during pump shutdown. The valves are selected or adjusted so that they open when the pressure differential falls through a predetermined range to augment diminished pumping capacity with a higher natural circulation flow rate.